The invention relates to a composite material in the form of a printed circuit board for electric circuits or modules and, in particular, to a composite material consisting of a ceramic or metallic substrate layer and a metallization formed from a thin metal plate or foil bonded to each of the surfaces of the ceramic or metallic substrate layer by an adhesive bond layer. The invention further relates to an adhesive bond material composed of nanofiber material in a synthetic matrix.
The manufacture of composite materials, also as printed circuit boards in the form of metal-ceramic substrates based on DCB technology is known in the art. In this process, the metallization required for the manufacture of strip conductors, connections, etc. is applied on a ceramic, for example on an aluminum-oxide ceramic, using direct copper bonding technology, the metallization being formed by metal or copper foils or metal or copper sheets, comprising on the top side a layer or coating (melt layer) from a chemical bond with the metal and a reactive gas, preferably oxygen.
In this method, which is described for example in U.S. Pat. No. 3,744,120 and in DE-PS 23 19 854, this layer or coating (hot-melt layer) forms a eutectic with a melting temperature below the melting temperature of the metal (e.g. copper), so that the layers can be bonded to each other by placing the foil on the ceramic and heating all layers, namely by melting the metal or copper essentially only in the area of the hot-melt layer or oxide layer.
This DCB method then comprises the following steps:                oxidation of a copper foil so as to produce an even copper oxide layer;        placing of the copper foil on the ceramic layer;        heating the composite to a process temperature between approx. 1025 and 1083° C., e.g. to approx. 1071° C.;        cooling to room temperature.        
Also known is the so-called active soldering method (DE 22 13 115; EP-A-153 618) for bonding metal layers or metal foils forming metallizations, in particular also of copper layers or copper foils, with the respective ceramic material. In this process, which is used especially for manufacturing a metal-ceramic substrate, a bond is produced at a temperature of ca. 800-1000° C. between a metal foil, for example a copper foil, and a ceramic substrate, for example aluminum-nitride ceramic, using a hard solder, which in addition to a main component such as copper, silver and/or gold also contains an active metal. This active metal, which is at least one element of the group Hf, Ti, Zr, Nb, Ce, creates a bond between the solder and the ceramic through a chemical reaction, while the bond between the solder and the metal is a metallic hard solder bond.
It is an object of the present invention to provide a composite material for printed circuit boards that can be manufactured in a simple and economical manner, while maintaining optimum thermal properties.